JPH01246A - Spheroidal graphite cast iron - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to high toughness spheroidal graphite cast iron.

[Prior art and problems to be solved by the invention] Conventional spheroidal graphite cast iron FCD37 or FC with ferrite base
D40 has some elongation and high impact value, but low impact value at low temperatures.

In order to improve these, a method of adding Ni@ was proposed in 1983.
-33897 etc.

However, in this invention, since the Bi content is 2.0% or more, an impact of at least 1.7 kof-m/cm2 at -15°C is applied.
゛Only the γ value can be obtained.

Recently, automotive and industrial casting parts are often used at temperatures as low as -40℃, and even at such low temperatures, they are still expensive!
I hit value is now required.

Therefore, the present inventors decided to reduce the Si content and to reduce the Bi content.
By adding a small amount of graphite particles, the number of graphite particles can be reduced to 300 particles/mm
By increasing it above, elongation and impact value were improved.

In addition, in the above invention, the condition is that the structure is ferritic, and in the embodiment, annealing is performed to form ferrite, but in order to reduce manufacturing costs, it is best to use the product in an as-cast state without performing annealing. preferable.

In the present invention, since a trace amount of Bi is added, the number of graphite grains increases, and the number of graphite grains decreases. The present invention was completed based on the finding that the value can be secured.

Of course, if annealing is performed to create a ferrite structure,
Needless to say, even higher elongation and toughness can be obtained.

The purpose of the present invention is to improve the elongation and impact value, especially the ** value at low temperatures, and to reduce manufacturing costs by omitting heat treatment or by only performing heat treatment at low temperature for a short time. It provides cast iron.

[Means for solving the problems] The spheroidal graphite cast iron of the present invention has the following characteristics: T1. m%CC: 3.0 to 4.0%Bi: 1.5
~2.3% Mn: <0.3% P: <0.03% Cr: <0.10% Ma: 0.02 ~ 0.06% CE value (carbon equivalent): 3.9 ~ 4.6 % residual iron and unavoidable impurities, and the molten metal having the above composition contains 0.0% residual iron and unavoidable impurities.
Add 0.05 to 0.03% of Bi, inoculate at the same time or after the addition of 81, and increase the number of graphite grains to 300 particles/m
m2 or more, and if necessary, the residual content of B1 is 0.0
015 to 0.0150%.

Next, the reason for limiting the above numerical values will be explained.

If C is less than 3.0%, castability deteriorates and the number of graphite grains decreases, resulting in an increase in pearlite.

Moreover, if it exceeds 4.0%, Quiche graphite tends to come out and the strength decreases.

If Bi is less than 1.5%, carbides tend to precipitate, resulting in a decrease in impact value and elongation. Moreover, if it exceeds 2 to 3%, the ** value and elongation will decrease due to the influence of silicoferrite.

When Mn exceeds 0.3%, pearlite increases and impact value and elongation decrease.

When P is 0.03%, the impact value and elongation decrease due to the influence of steadite.

When Cr exceeds 0.1%, carbides tend to precipitate, resulting in a decrease in impact value and elongation.

If MO is less than 0.02%, graphite will not become spheroidized, and 0.06%
If it exceeds %, not only shrinkage cavities and carbides are likely to appear, but it is also economically disadvantageous.

If the CEI is less than 3.9%, carbides tend to appear and castability deteriorates. If it exceeds 4.6%, quiche graphite tends to appear.

When the residual content of B1 is less than 0.0015%, the effect of increasing the number of graphite grains decreases, and as a result, cementite is generated in the as-cast structure.

Furthermore, if the residual content exceeds 0.0150%, the effect of Bi on inhibiting graphite spheroidization appears, the spheroidization rate of graphite becomes 70% or less, and various mechanical properties deteriorate.

Since Bi has a poor melt penetration yield rate for spheroidal graphite cast iron molten metal and has large fluctuations, its residual content should be reduced to 0.
In order to make it 0.0015% to 0.0150%, it is necessary to set the addition amount to 0.005% to 0.030%.

If the number of graphite particles is less than 300 particles/mm2, the distance between graphite particles becomes large, pearlite precipitation increases, and the impact value and elongation decrease.

[Function] According to the present invention, spheroidal graphite cast iron having high elongation and high impact value, especially high impact value at -40°C, can be obtained even when as-cast.

・If you perform ferrite annealing heat treatment, even higher impact value and elongation can be obtained.

[Example, 1] 1>Chemical components
(wt%) 2) Mold 25mm thick x 250mm long Y block mold C
It was molded using an O2 mold.

3) Results The results of the investigation on test pieces made by pouring molten metal into the mold described above are described below. .

Microscopic structures are shown in FIGS. 1(a), (b), (c), and (d). The material of the present invention shown in FIG. 1(a) has a large number of graphite particles,
It can also be seen that there is a large amount of ferrite. In comparison, the normal FCD40 shown in FIG. 1 (1)) has fewer graphite grains and more pearlite.

Further, the low $1% FCD40 shown in FIG. 1(C) has a small number of graphite grains and an extremely large amount of pearlite.

It can be seen that in the ordinary FCD40 shown in FIG. 1(d) to which Bi was added, the number of graphite grains increased and the amount of ferrite also increased.

Figures 2 and 3 show the mechanical properties. Although the tensile strength and yield strength of the present invention material are lower than those of FCD40, the elongation and impact values are good, especially at -40℃t'1, about 7kOf/ve2 (1). value is obtained.

In addition, FCD40r with low Si has a high tensile strength and proof stress due to the large amount of pearlite in the microscopic structure, but it elongates and the Wγ value becomes significantly low. Further, in the microscopic structure of normal FCD with St% added with B1, graphite is refined and ferrite is increased, but compared to the low-Si material of the present invention, it is elongated and has a low impact value. In particular, no significant improvement in the low temperature impact value at -40°C was observed.

In this way, it can be seen that the material of the present invention is significantly superior to conventional materials or conventional materials that have been improved by lowering Bi or adding Bi.

It can also be seen that excellent materials can be obtained without heat treatment.

[Effects of the Invention] As is clear from the above explanation, the spheroidal graphite cast iron of the present invention has excellent tensile strength, elongation, and impact value in the as-cast state as described above, but when heat treated, Compared to as-cast materials, it has even better elongation and improved impact values, especially at low temperatures.

That is, it brings about a remarkable effect in improving the mechanical properties of spheroidal graphite cast iron and reducing manufacturing costs.

[Brief explanation of the drawing]

Figures 1 (a), (b), (c), and (d) are metallurgical microstructure photographs, and Figures 2.3 and 2.3 both show mechanical properties.

Claims (2)

[Claims] (1) In weight% C: 3.0-4.0% Si: 1.5-2.3% Mn: <0.3% P: <0.03% Cr: <0.10% Mg: 0 .02 to 0.06% CE value (carbon equivalent): 3.9 to 4.6% 0.005 to 0.03% Bi is added to the molten metal containing residual iron and unavoidable impurities and having the above composition. , the number of graphite grains was reduced to 30 by inoculating at the same time as or after the Bi addition.
Spheroidal graphite cast iron with a density of 0 pieces/mm^2 or more. (2) Spheroidal graphite cast iron according to claim 1, wherein the Bi content is 0.0015 to 0.0150%.